With his campaign backed by many top state and national Democrats, U.S. Representative Patrick Murphy was among the first candidates to formally submit candidacy papers and a check to run for the U.S. Senate as pre-qualifying opened at the Division of Elections on Monday.

A Mason-Dixon poll released Monday gave Murphy a 31 percent to 23 percent edge over fellow Congressman Alan Grayson in the Democratic primary.

Labor attorney Pam Keith drew three percent.

Murphy, a two-term Congressman representing the Treasure Coast area, remains unknown to many Floridians as do most of the other major Senate candidates from both parties.

"I think as people start looking, you know, beyond the presidential, as there is more clarity as to who the nominees are, people will start to look down ballot," he said. "We're doing the best we can. I do as many events a day as I think humanly possible trying to meet voters."

The poll of 625 registered voters also found nearly half of those likely to vote in the primary election want Republican U.S. Senator Marco Rubio to go back on his pledge of not running for re-election.

Despite urging from GOP leaders and favorable new polling numbers, but at an appearance Monday in Orlando with Sen. Bill Nelson, he said he’s still not running.

“Nothing’s changed from what I’ve said previously and I don’t have anything new to announce on that other than one of the great parts of this is job is to have worked alongside Senator Nelson," said Rubio.

Florida Lieutenant Governor Carlos Lopez Cantera is making a bid for a bigger job: representing Florida in the U.S. Senate. Lopez-Cantera has announced he was to succeed current Florida Senator Marco Rubio, who is running for President.